How birds handle the ‘lights out’ during an eclipse

By Joan Collins

A once-in-a-lifetime celestial event will envelope the Adirondacks in darkness on April 8. Now’s a good time to ponder endogenous biological clocks and how birds might react to their world suddenly seeming like night in mid-afternoon. Scientists are particularly interested in this total solar eclipse since it will occur during early spring bird migration.

Circadian rhythm is the 24-hour internal clock that regulates behavior for plants, animals, fungi and bacteria, allowing organisms to anticipate sunrise or sunset. This evolutionary biological clock is essential for aligning behavior with the environment.

Light and dark are the strongest external cues that influence circadian rhythms, but other daily changes, including temperature, and in some animals, such as birds, magnetic field and barometric pressure also play roles.

Humans have been bucking their biological clock since the creation of light: first with fire, then candles, oil lamps, kerosene lamps, electric bulbs, fluorescent lights, to LED illumination. Earth is now awash in bright artificial light easily observed from planes or outer space.

Our natural rhythms are continuously disrupted resulting in negative health outcomes.

Scientists have been collecting information on what happens to wildlife with a disruption to their routines during total solar eclipses, particularly during the past hundred years. Technology of the 21st century has advanced data collection and observations from sharp-eyed citizens. Some of the variables from prior eclipses include location in the world, time of year and time of day. 

When day becomes night

A total solar eclipse occurred during a late summer afternoon on Aug. 31, 1932 in the Northeast. Chickens, pigeons and flocks of daytime migrating common nighthawks went to roost. Diurnal birds fell silent during totality and nocturnal birds such as owls and whip-poor-wills vocalized. Shorebird flocks were observed taking flight high over the ocean and did not return after totality, with an assumption these nocturnal migrants headed out with the “night” cue of darkness.

Researchers made similar observations during a winter eclipse in Manitoba on Feb. 26, 1979. Three hours after sunrise, diurnal birds went to roost as it became dark, and great horned, snowy and great gray owls started hooting and feeding. Birds left feeders as totality approached including Canada jays that left eight minutes before dark and came back 11 minutes after the sun reappeared. A bohemian waxwing roosted with its bill tucked into its scapular feathers. Many birds sang as the sun reappeared as if it was dawn.

On the north coast of Venezuela during an eclipse on Feb. 26, 1998, magnificent frigatebirds and brown pelicans left the bay to roost. Royal terns disappeared. Laughing gulls ceased foraging and flew rapidly in a tight flock back and forth over the water during the few minutes of darkness. The birds resumed foraging over the water 12 minutes after totality.

In the total eclipse of Aug. 21, 2017, beginning at the West Coast in the morning and finishing at the East Coast in late afternoon, researchers collected information from radar and eBird reports. Diurnal species such as vultures, herons and magpies were observed flocking to roosts. Some night-migrating warbler species began to give nocturnal flight calls.

Aerial insectivores, such as swallows, swifts and migrating purple martins and common nighthawks, descended to roost. Purple martins, silent during totality, excitedly vocalized and flew off high as the light returned. Barred, great horned and eastern screech owls began to vocalize. Radar showed skies emptying of birds and insects as darkness approached, and skies filling as totality ended. 

April 8 is early for spring migration in the Adirondacks. But many species will have returned including sandhill cranes, American woodcocks, northern saw-whet owls and winter wrens. Canada jays and winter-irruptive pine siskins will be nesting. Crossbill species will be finishing their winter nesting. If the weather is warm enough, amphibians will start singing when the skies darken.

Citizens may collect information during the eclipse for the Cornell Lab of Ornithology’s worldwide database, eBird, and the iNaturalist.

At our home we plan to have cameras on our front and back platform bird feeders to capture sound and video. I have already picked one of my favorite wildlife locations to be during the event.

Whether out collecting wildlife data, or just enjoying the eclipse, I hope you can experience this rare phenomenon.